Blair Blakie, a physicist researching ultra-cold gases at the
University of Otago, responded.

A bubble is a gas pocket in some other substance which could
be either a liquid or a solid. Usually when we think of bubbles
what comes to mind is spherical film of liquid filled with air,
as in a soap bubble. Some common examples of bubbles that occur
in bulk liquids are carbon-dioxide bubbles in fizzy drinks, and
the bubbles of steam that form in boiling water.

A well-known solid that contains bubbles is pumice rock, which is
commonly used cosmeticically to remove rough skin. Pumice rock is formed from
explosive volcanic eruptions in which the ejected liquid lava
contains many bubbles that are frozen into the rock when it solidifies.

Bubbles feature in cutting edge scientific studies, such as the phenomenon
of sonoluminescence (literally 'sound-light'), which is the emission of
light by bubbles in a liquid excited by sound. The sound waves compress
the bubbles and in some circumstances the bubbles may implode and give
off energy in the form of light. Scientists believe that the temperature
during collapse may be more than 10,000 degrees Celsius (some estimates
suggest temperatures higher than a million degrees) and could provide
conditions suitable for nuclear fusion to take
place - the same process that occurs in the Sun. An experiment in 2002
has reported some evidence for fusion using sonoluminescence, but these
results are still highly debated in the scientific community. Perhaps
bubbles will provide an answer to our future energy needs?